Desalting of mineral oil



Jan. 9, 1945. c. G. KIRKBRIDE DESALTING OF MINERAL OIL Filed May 27,1942 oil to dewaxing procedures.

Patented mi 9 1945 Premi ortica 2,366,792 DESALTIN G F MINERIL OHLChallmer G. Kirkbrille, Texas City, Tex., Ias signor to llan AmericanReg Corporation, Texas City, Tex.; afcorporatlon of Delaware ApplicationMay 27, 1942, Serial No. .444,711

' 13 claims. (o1. 252-348) This inventionvrelates in general to thedesalting of mineral oil and more particularly has reference to theseparation of salt in the form of a wax-salt water mixture by subjectingthe Crude oil contains salt in varying degrees, depending on the eld andthe nature of the strata from which the Acrude is obtained. `The saltcontent may varyirom wzero to values as high as 100 grams per barrel oreven higher. for example, the amount of saltv in East Texas may varyfrom about to 20 gramsfper barrel, whereas for Cayuga crude the saltcontent may be about 80 grams per barrel or higher. The variation insalt content will also depend on the season of .the year, the saltcontent being higher during the winter season when it is more difiicultto separate the salt water from the crude. This salt or saltwater in thecrude is the cause of corrosion and also fouling of heat exchangers,furnace tubes, and parts of the distillation equipment. Also inthe caseof -catalytic cracking, it has a. detrimental eiect on catalyst activityand life. It is, therefore, apparent that the salt in crude oil is anobjectionable impurity-and many procedures have been developed for Vitsremoval. Fortunately, it is not necessary to completely remove the saltinasmuch as salt contents aslow as 2 grams to 3 grams per barrel usuallywill not cause significant damage to the catalyst or fouling of heatexchangers, furnace tubes. etc.

Salt in crude oil isan objectionable impurity and many procedures forits removal have been developed. While some of these procedures areeffective they involve extensive manipulations land add to the cost ofthe products to be made from the crude oil.

Wax is another undesirable impurity present in various proportions incrude oils from various sources and many procedures have been proposedfor eiecting the .dewaxing of such oils. Inv most instances the dewaxingis not eiected from the crude oil but from partially rened oil and afterdesalting.

A maior object o'f this invention is the desaming of crude oil. I

Another object rifthis invention is to effect simultaneous desalting anddewaxing of crude oil.. A further object of this invention is to providea method of desalting crude oil by precipitating yexisting orf addedlwax in the i'orm of separable wax-salt water mixtures and separating theprecipitated material from the oil.

Still another object of this invention is to provide a method ofdesaltingL crude oil by heating the oil to above atmospheric..temperature, adding wax thereto', cooling the oil to atmospherictemperature to eiect precipitation Aof the wax together with saltwateradmixed therewith and separating the precipitated mixture.

`A still further object of this invention is to provide a method ofdesalting crude oil by precipif tating existing or added wax in the formof septhe oil.

arable wax-salt water mixtures, separating the wax from the salt, andrecovering the separated wax for further use in desalting.

Yet another object of this invention is to provide a method of desaltingcrude oil'by precipitating existing or added wax in the form ofseparable wax-salt water mixtures by cooling the oil by expandingcontained or added liqueed light hydrocarbon fractions and separatingthe precipitated material from the oil. l

With these and otherA objects in view which will appear hereinafter, theinvention embodies generally 'the stepsv of separating existing or addedwax along with the salt from salt containing crude oil by cooling theoil to a temperaturel at which the wax-salt water mixture or emulsionwill precipitate and then separating the mixture .or emulsion from theoil.

In order to facilitate an understanding of this taining wax crystals isallowed to stand, the wax crystals will settle and the bottoni layerformed g principally of wax will also have a very much higher saltcontent than the remaining portion of For instance, in the case of East`Texas crude oil, the salt content of the wax layer obtained afterstanding might be as high as 3000 to 5000 grams per barrel. On the otherhand, in crude oils not having a high wax content such as those obtainedfrom Hastings and South Houston, the salt water remains to a largeextent in the form ot an emulsion and mere settling may. not greatlyreduce the salt content of the oil.

It is believed that the settling of the wax crystals entrains smalldroplets of salt Water to form a mixture or emulsion and when the Wax ofthe crude oil. The salt particles or salt water y particles may act asnuclei for thecrystallization of wax such that when the wax iscrystallized, the

greater proportion of thev salt water nuclei are entrained during theprecipitation of a relatively small Yportion of the total wax content ofthe i crude oil. It has been ascertained by microscopic examinationsthat the wax crystals settled from the oil actually enmesh the saltwater particles. In one particular instance it was found that crude `oilcontaining about 40 grams of salt per barrel had its salt contentreduced by the separation of the wax therefrom to about 0.

In the case ofl crude oils having a low wax content such as thoseobtained from Hastings and South Houston, the salt water content canstill be removed in accordance with the present invention by addingcrystalline wax to the crude,

. thereby increasing its Wax content to such a point that whencrystallization is eiected, sucient salt solution will be entrained inthe Wax crystals to elect the removal ,of a considerable portion of thesalt water solution content.

In the case of crude oils having a small wax content and in which itwould be impractical to cool to a suciently low temperature toprecipitate the wax, the crude oil is heated to a temperature somewhathigher than atmospheric, and preferably to a temperature sufficient toplace the Wax in true solution, usually 125 to 140 F.'

which is added should be preferably of relatively high melting point inorder to facilitate its precipitation without necessitating extremelylow cooling temperatures. If the amount of added wax is suiciently highin quantity and has a high melting point, it is possible to effect thedesired crystallization by merely cooling to atmospheric temperature andavoiding the necessity of refrigeration equipment. However, in order toavoid the necessity of adding extremely large quantities of Wax, someform of moderate refrigeration, for example, cooling to 50 F. which canbe easily and economically effected with vacuum jet refrigerationequipment, is advantageously adopted. Following the addition of theproper quantity and kind of wax, the crude oil is then cooled toatmospheric temperature or lower if necessary and the Wax whichwasvplaced in solution at the higher temperature' will then beprecipitated and during the precipitation will entrain the salt waterand thereby effectively desalt the crude. The mixture or emulsion of waxand salt water may be removed either by settling andldecantation or byfiltration.

vIn cooling the crude oil to effect precipitation of the wax and theentrained salt water, various refrigeration means may be employed. It isalso within the concept of the present invention to eifect internalrefrigeration of the crude oil by evaporation of a portion of the crudeoil itself, that is, evaporation. of some of its lighter constituents.In this connection the crude oil would be passed or injected into achamber maintained at subatmospheric pressure in which the lighterfractions of the crude oil would be immediately vaporized. The latentheat required for vapori'zation of light fractions cools the liquidportion of the crude oil to a suiiiciently low temperature at which thewax crystals will precipitateand entrain the particles of salt water.

The so treated unvaporized portion of the crude Voil will then be passedinto a zone in which the wax crystals and salt water may be settled outor the cooled liquid portions of the crude may be subjected tofiltration for removal of the wax crystals and the entrained salt water.This method of refrigeration is particularly applicable to crude oilshaving a fairly high vapor pressure such as is the case of East Texascrude oils.

'I'he reduced pressure in the low pressure or flash chamber may bemaintained by any suitable means such as vacuum pumps or electors. Also,the vapors removed from the crude oil in the zone of reduced pressuremay be recovered by absorption, adsorption, or compression followed bycondensation or any other method suitable for such recovery of thevapors. A reduced pressure may be maintained in the reduced pressurezone by the use of gas oil in a jet or barometric leg and the gas oil.would also serve as an absorbing medium for the vapors evolved from thecrude. f

In some cases -Where the viscosity ofthe crude oilis' very high underthe reduced filtering or settling temperatures, a light naphtha cut maybe added for the purpose of reducing the viscosity to a point wherefiltration will be facilitated. The light naphtha added will also aid inany settling operation inasmuch a's it will increase the difference ingravity between the cooled crude oil and the salt-wax mixture.

In lieu of internal refrigeration by evaporation of the lightconstituents of the crude oil in a vacuum chamber, internalrefrigeration of the crude oil may be obtained by cycling or recycling anormally gaseous hydrocarbon such as propane along with the crude oil.In this instance, liquid propane is added to the incoming crude oil andthen allowed to evaporate. The heat of vaporization of the propane willcool the crude oil suiciently to precipitate the existing or added waxtherein and as in the preceding instances will entrain the salt watercontained in the crude oil. The propane may be recovered by compressionand condensation and re-cycled in the process.

Referring to the accompanying drawing, there is shown a system fordesalting crude oil utilizing both internal refrigeration and re-cyclingof wax. As shown in the drawing, the salty crude oil is pumped to astorage container I from which it is drawn by the pump 2 and forcedthrough conduit 3 into the low pressure zone 4. A reduced pressure ismaintained in the zone 4 by means of the pump 5 which draws gas andvapors from the upper portion of zone 4 through the conduit 6.

The salt containing crude oil is pumped from the storage tank into thelow pressure zone and may be ejected into said zone in such a manner asto effect a flashing or vaporization of the lighter constituentsthereof. As explained above,

' the flashing of the crude oil will effect internal refrigeration ofthe non-vaporized portions which will collect in the lower regions ofthe zone 4. The cool liquid portions of the crude oil together with theprecipitated Wax and entrained salt water are then drawn from the zone 4`by means of a suitable pump 1 into a filter 8 iny which thecrystallized wax particles together with the entrained salt water areseparated from the oil. The desalted crude is then discharged throughthe conduit 9 to a storage vessel (not show n).

Filter 8 may be of any suitable type effective for the purpose and thewax and entrained salt water separated in the lter are discharged into aheating zone I containing a heating coil II.`

In the heating zone IU, the mixture of wax and salt water is heated tomelt the wax and the mixture of liquid wax and salt water is passedthrough conduit I2 into the wax settler I3. From the lower portion ofthe settler vI3 the salt water is drawn o and from an upper portionthereof the wax portion is discharged through conduit I d. Of the waxremoved from the Wax settler I3, a

portion is re-cycled for introduction into thel conduit 3 for conductingthe crude oil to be treated into thevlow pressure zone d. This wax inliquid form is introduced through conduit I5. Wax discharged throughconduit I6 in excess of that required for re-cycling is discharged fromthe system through conduit Iii.

In the event of Ain suilicient wax in the crude further wax may be addedthrough conduit 28.

If desired, the cooled desalted crude discharged through conduit 9 maybe passed in heat exchange relation with the crude oil prior tointrdduction of the crude into the reduced temperature zone. 'For thispurpose the cold desalted oil is passed through conduit I7, to thecooling heat exchanger I8 and thence through conduit I'Ia to storage.

If the temperature of the crude oi'l to be desalted and requiring theaddition of further wax for desalting is too low to receive additionalwax,

convection currents therein.

the lcold oil may be passed through a heat ex- I changer I9 which isheated by a suitable medium.

This will heat the cold crude oil to a temperature high enough todissolve the desired quantity of added wax.

If the crude has already been stripped of its lighter fractions prior tothe desalting treatment, or if insufcient internal refrigeration isobtained by flashing the crude, a normally gaseous hydrocarbon such aspropane in the liquid phase may be introduced into the crude oil. Asindiwithdrawn from Ythe ash chamber or low pressure zone 4 by compressor5, compressed and passed through conduit 2| which includes a condenser22. The condensed liquid propane is then re-cycled through conduit intothe system.

It is also within the concept of the present invention to effect thedesalting of crude oil by entraining the salt water in precipitated waxcrys' tals, permitting settling of the precipitated waxv crystals in aquiescent zone, and then melting the settled wax layer without settingup substantial For this purpose a crude o'il containing the precipitatedwax and entrained saltwater may be run through a conduit 23 into aquiescent zone 2d in which the wax is allowed to settle. After settlingof the wax asrindicated at 26, the salt free oil together with the waxbeing drawn oi at 21.

- While I have shown methods of separation involving generally the useof a settling operation or -a lter, other known methods of separatingthe crude oil from the salt-wax mixture may be used. For example,centrifugal separating means may be used. In this case, the mixture fromthe flash chamber 4 would be pumped to a regular centrifuge where thewax and salt water would be removed from the crude oil. In suchk anoperation, by introducing hot water into the wax-salt water stream, thesalt water may be diluted and the wax melted so that the mixture leavingthe centrifuge can be separa-ted into its in the wax.

-In those instances in which wax is added to a crude oil having a lowwax content, the added wax should be`of such a nature Aas to be easilyseparated from the oil upon precipitation. Like- Wise, the wax selectedshould have properties, which will facilitate the entrainment of thesalt;

water contained in the oil. f

From the foregoing description it will be appreciated that the presentinvention provides several procedures for effectively desalting crudeoil by removing existing or added wax and salt water entrained thereinor by merely effecting settling oil at above atmospheric temperature,cooling said mixture to precipitate solid wax and entrained salt,separating the wax and entrained salt from the oil, recovering desaltedoil, and

.eifecting separation between the wax and the entrained salt.

2. A method of desalting 'crude mineral oil which comprises maintainingan intimate mixture of iluid wax and salt-containing mineral oil atabove. atmospheric temperature, cooling said I mixture to precipitatesolid wax having salt enwax, the oil is heated from a coll 25 or othersource positioned above the wax layer so that the wax layer will bemelted sulciently to free the entrained salt water without creating.sufiicient convection currents to agitate themelted wax and salt watersuilicientlmto again mix the same.. Under these conditions. the freedsalt water would settle out at the bottom of thezone and-may be drawn oifrom the layer of melted trainedA therein, separating the wax and en-Avtrained salt from the oil, recovering desalted oil, effecting separationof the wax and the entrained salt, and commingling substantiallysaltfree wax with additional amounts of salt-containing crude mineraloil.

3. A method of desalting crude mineral oil comprising adding waxthereto, cooling the oil to effect precipitation of the Wax containedtherein in admixture with salt and separating the precipitated material.

4. A method of removing salt from crudemineral oil comprising heatingthe same to a temperature below that at which low boiling fractions willseparate, adding crystallizable wax to the heated oil, cooling the waxcontaining oil to precipitate wax crystals admixed with salt andseparating the precipitated crystals. 5. Ame'thod of ydesalting crudeminerai oil comprising introducing a liquefied normally gaseoushydrocarbon into the wax land salt containing mineral oileiectingevaporation of the added hydrocarbon to chill the mineral oil andprecipitating a mixture of the wax and salt and separating'theprecipitated waxsalt emulsion.

6. A method of desalting crude mineral oil comprising heating the oil toa temperature 'above atmospheric, dissolving a quantity of Wax therein,cooling the oil to atmospheric temperature to eiect a ,precipitation ofthe added Wax in the form of a salt water entrainingcrystals and thenseparating the precipitated material.

V'7. Armethod of desalting crude mineral oil having a high vaporpressure and containing precipitatable Wax comprising passing the oilinto a zone at a reduced pressure to eiect vaporization of the lightportions of the oil and consequent refrigeration thereof, therebyprecipitating the wax in the form of salt Water entrained crystals andseparating the precipitated material.v

8. A method of desalting crude mineral oil comprising passing the,oilunder pressure into.

a zone of reduced pressure vto cause the light fractions thereof toVaporize with consequent cooling of the remaining liquid portions of theoil and precipitation of wax crystals mixed with salt, separating theprecipitated crystals, heating the separated mass 'to separate the Waxfrom the salt water, and mixing the separated Wax with fresh portions fcrude mineral oil to be desalted prior tol cooling Aof the same.

9. A method'of removing salt strom crude mineral oil comprising heatingthe oil to a tem. perature below that at which low boiling fractionswill separate, adding Wax to the heated oil, cooling the wax containingoil and expanding the same into a zone of reduced pressure to of the oiland to effect precipitation of wax in the form of crystals entrainingsalt, and circulating the cool wax-free and salt-free oil in `'heatexchange relation with the oil to be treated after addition of waxthereto to eect pre-cooling of the oil to which the wax has lbeen added.

11. A method .of removing salt from crude mineral oil comprising heatingthe oil to a temperature below that at which low boiling fractions willseparate, adding wax to the heated oil, cooling the wax containingoil-and expanding the same into a zone of reduced pressure to effectfurther cooling of the unvaporized por- 'tions of the oil and to effectprecipitation of wax in the form of crystals entraining salt,

treating the separated wax andsnalt water material to separate the waxfrom the salt Water, and re-introducing the wax into crude oil -to betreated prior to cooling thereof.

12@ A method of desalting crude mineral oil comprising cooling the oilto effect precipitation of wax crystals containing entrained salt water,effecting `settling of the precipitated material and heating the settledlayer of the precipitate in a manner to avoid substantial convectioncurrents to melt the wax of said settled layer and then separating thesalt water fromy the melted layer of wax. I

13. The method of desalting crude mineral oil which comprisesintimately-mixing liquid wax and salt-containing mineral oil, coolingthe ineffect further'cooling of the unvaporized porf tions of the oiland to eiect precipitation of Wax in the form of crystals entrainingsalt,

Vand separating the lprecipitated crystals.

timate mixture sufilcient to precipitate solid wax with entrained salt,separating` solid wax and entrained salt from said mineral oil, andrecovering the desalted oil.

CHALMER (3. KIRKBRIDE.

